Hopper, or bin, screw feeder construction controlling discharge velocity profile

ABSTRACT

A bin or hopper, preferably with one-dimensional convergence, has a slot outlet at its bottom for discharging bulk solid particulate material (such as coal, wood chips, sugar, plastic pellets, etc.) to a screw in a trough. The screw has varying flight diameter, shaft diameter, and average pitch along its length to a discharge so as to provide substantially uniform material flow velocity distribution along the slot outlet. One or more flow rate adjusters may regulate flow of material being transported by the screw. Each flow adjuster may be a vertical plate with a substantially straight-across bottom curved about a substantially horizontal axis, or with a bottom two-dimensional curvature.

CROSS REFERENCE TO RELATED APPLICATION

This application is based upon U.S. provisional application Ser. No.60/080,824 filed Apr. 6, 1998, the disclosure of which is incorporatedby reference herein.

BACKGROUND AND SUMMARY OF THE INVENTION

In handling and processing of bulk solids such as sugar, coal, drinkmixes, wood chips, and various plastics (typically pellets) in a bin orhopper, it often becomes essential that the solids velocity profileacross any section of the bin and/or hopper be uniform so that the binor hopper produces a first-in/first-out flow sequence. When this flowsequence is achieved, then processing requiring gas or liquidcounterflow or concurrent flow have the opportunity to maximize theirefficiency. Problems of segregation of different particle sizes can besubstantially eliminated and interfaces between batches of product inthe same bin can be clearly defined. Achieving such a result requiresthat the feeder and the hopper act in unison to produce the flowuniformity desired. The larger the hopper outlet, the more sensitiveflow uniformity is to the feeder design. The present invention addressesthe design of a screw feeder under a slot and the associated hopper toproduce the uniform flow velocity distribution desired.

Prior screw feeder art has focused mostly on compaction or extrusionscrews (e.g. U.S. Pat. No. 5,052,874). No attempt has been made tointegrate the workings of the screw and the hopper to control solidsflow patterns. As a result, the flow from a hopper or bin is somewhatunpredictable and not suited to fully effective solids processing.

According to one aspect of the present invention a bin or hopperdischarge assembly is provided comprising the following components: Abin or hopper having at least one bottom slot outlet of effective lengthL. At least one screw in a trough and rotatable with a screw shaft ofdiameter d and having flights with a flight diameter f, and an averagepitch P and an effective length substantially equal to L, the screwreceiving material flowing through the at least one slot outlet, andhaving at least one (preferably only one) discharge from the screwtrough. The screw having a varying average pitch, shaft diameter, andflight diameter, and an effective length L; and the screw constructed tocorrespond to the formula$\frac{{\left\lbrack {\left( f_{n + 1} \right)^{2} - \left( d_{n + 1} \right)^{2}} \right\rbrack P_{n + 1}} - {\left\lbrack {\left( f_{n} \right)^{2} - \left( d_{n} \right)^{2}} \right\rbrack P_{n}}}{\left( {P_{n} + P_{n + 1}} \right)/2} = \frac{\left( {f_{L}^{2} - d_{L}^{2}} \right)P_{L}}{L}$

where f_(n), d_(n), and P_(n) are the flight diameter, shaft diameterand pitch of the screw at the nth pitch increment along the length L,and f_(L), d_(L), and P_(L) are the flight diameter, shaft diameter, andpitch of the last or final pitch increment under the flow outlet nearthe screw discharge. The bin or hopper preferably is one havingone-dimensional convergence.

The assembly preferably further comprises at least one flow rateadjuster mechanism which provides flow regulation of materialtransported by the screw. For example, the adjuster mechanism maycomprise a substantially vertical plate with a substantiallystraight-across bottom curved about a substantially horizontal axis.Alternatively, the adjuster mechanism may comprise a substantiallyvertical plate with a bottom having two-dimensional curvature. In bothcases the plate's axial positions are adjustable over a part of thelength of the screw, and also may be vertically adjustable. The flowrate adjusters may also be used with screws having uniform pitch, shaftdiameter and flight diameter.

The at least one screw may consist of a single screw, and the at leastone slot outlet may consist of a single slot outlet, and the at leastone discharge may consist of a single discharge. The screw typically hasfront and back ends, and the at least one flow rate adjustment mechanismmay comprise an adjustment mechanism at each of the front and back ends.

Alternatively, the at least one slot outlet may comprise first andsecond slot outlets, the at least one screw comprises a right hand screwcooperating with the first slot outlet and a left hand screw cooperatingwith the second slot outlet, the screws on a common shaft. In this casethe at least one discharge may comprise a single common protecteddischarge between the first and second slot outlets, and a hangerbearing may be provided for the shaft adjacent the protected discharge.The first and second slot outlets are preferably in intermediateone-dimensional convergence hoppers beneath a larger long slot outlethopper with one-dimensional convergence. The flow rate adjustermechanism may be mounted adjacent an end of each screw opposite thecommon discharge.

Alternatively, the at least one screw consists of a single screw, andwherein the at least one slot outlet comprises more than two slotoutlets from more than two intermediate one-dimensional convergencehoppers beneath a larger long slot outlet hopper with one-dimensionalconvergence, the more than two slot outlets collectively having theeffective length L, the more than two slot outlets each cooperating withthe single screw. Preferably, the at least one discharge comprises asingle discharge, and a flow rate adjuster mechanism is associated witheach of the more than two slot outlets. Typically, the bin or hoppercontains, and feeds with a substantially uniform flow velocitydistribution along the slot outlet, coal, wood chips, plastic pellets,sugar, or drink mixes, or like bulk solid particulate material.

According to another aspect of the present invention a bin or hopperassembly is provided comprising: A bin or hopper having at least onebottom slot outlet of effective length L. At least one screw in a troughfor receiving material from the at least one slot outlet and having aneffective length substantially equal to L. The at least one screwrotatable with a screw shaft having a diameter, and having flights witha flight diameter and an average pitch. A single discharge from the atleast one screw trough. And at least one flow rate adjuster mechanismwhich provides flow regulation of material transported by the screw. Thescrew shaft diameter, flight diameter, and average pitch preferablyvarying along the shaft length so as to provide a substantially uniformmaterial flow velocity for distribution along the slot outlet. The binor hopper preferably has one-dimensional convergence.

According to yet another aspect of the present invention a bin or hopperdischarge assembly is provided comprising: A bin or hopper having atleast one bottom slot outlet of effective length L. At least one screwin a trough and rotatable with a screw shaft and having flights, and anaverage pitch, and an effective length substantially equal to L, thescrew receiving material flowing from the at least one slot outlet. Atleast one discharge from the screw trough. And the screw having avarying average pitch, shaft diameter, and flight diameter, and aneffective length L, providing a substantially uniform flow velocitydistribution along the slot outlet of solid particulate material flowingfrom the bin or hopper to the screw discharge. The bin or hopperpreferably has one-dimensional convergence.

According to still another aspect of the invention an assembly isprovided comprising: A bin or hopper (preferably having one-dimensionalconvergence) having at least one bottom slot outlet of effective lengthL. At least one screw in a trough for receiving material from the atleast one slot outlet and having an effective length substantially equalto L. The at least one screw rotatable with a screw shaft having adiameter, and having flights with a flight diameter, and an averagepitch. A single discharge from the at least one screw trough. The screwhaving a varying average pitch, shaft diameter, and flight diameteralong the length thereof, and wherein the screw varying average pitch,shaft diameter, and flight diameter provide a substantially uniform flowvelocity distribution along the slot outlet of solid particulatematerial flowing from the bin or hopper to the screw discharge.

It is a primary object of the present invention to provide enhanceduniformity of flow velocity distribution from a hopper or bin using aparticular screw feeder. This and other objects of the invention willbecome clear from an inspection of the detailed description of theinvention and from the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic isometric view of a first embodiment of a bin orhopper assembly according to the present invention with part of thescrew trough cut away for clarity of illustration;

FIG. 1B is a bottom plan view of the bin or hopper of FIG. 1A, showingthe slot outlet thereof;

FIG. 2 is a schematic isometric view like that of FIG. 1A only for anembodiment of an assembly according to the invention having adjustableflow regulation;

FIGS. 3A-3D are an end view (in association with the screw of FIG. 2),side view, top plan view, and isometric view, respectively, of a firstembodiment of a flow adjuster useable in the assembly of FIG. 2;

FIGS. 4A-4C are end (in association with the screw of FIG. 2), side, andtop plan views, respectively, of a second embodiment of a flow adjusteruseable in the assembly of FIG. 2;

FIG. 5 is a view like that of FIG. 2 of an embodiment according to theinvention having first and second opposite hand screws associated withslot outlets of two intermediate hoppers with one-dimensionalconvergence; and

FIG. 6 is a view like that of FIG. 2 of an embodiment having a singlescrew and a plurality of intermediate hoppers each with a slot outlet.

DETAILED DESCRIPTION OF THE DRAWINGS

The simplest form of the invention is a single continuous specificallydesigned screw 1 shown in FIG. 1A under a preferably one-dimensionalconvergence hopper 2. The hopper has a slit outlet 2′ (see FIG. 1B). Thescrew 1 has a variable shaft 3 diameter, variable pitch 4, and screwdischarge 5. One dimensional hoppers are shown per se in U.S. Pat. Nos.4,958,741, 5,500,083, 5,617,975, and 5,628,873 and U.S. StatutoryInvention Registration H1681, the disclosures of which are incorporatedby reference herein. Substantially uniform flow along the effectivelength of the screw 1 is achieved by varying the average pitch P, shaftdiameter d (see FIG. 3A) and flight diameter f (see FIG. 4A) along theeffective length L of the screw 1 under the hopper outlet 2′ ofeffective length L as follows:$\frac{{\left\lbrack {\left( f_{n + 1} \right)^{2} - \left( d_{n + 1} \right)^{2}} \right\rbrack P_{n + 1}} - {\left\lbrack {\left( f_{n} \right)^{2} - \left( d_{n} \right)^{2}} \right\rbrack P_{n}}}{\left( {P_{n} + P_{n + 1}} \right)/2} = \frac{\left( {f_{L}^{2} - d_{L}^{2}} \right)P_{L}}{L}$

where f_(n), d_(n), and P_(n) are the flight diameter, shaft diameterand pitch of screw 1 at the nth pitch increment along the length L, andf_(L), d_(L), and P_(L) are the flight diameter, shaft diameter, andpitch, respectively, of the last or final pitch increment under theoutlet 2′ near the screw discharge 5.

The screw 1 designed in this manner will generally provide asubstantially uniform flow into the screw 1 along its effective length.However, with chunky materials, like coal or wood chips, and withstringy or springy materials, like bark, shavings, or wood chips, flowinto the ends of the screw 1 does not completely fill the flights unlessan adjustment is made to allow for a more complete filling. Thisadjustment is the next complication to the invention and is illustratedin FIG. 2.

FIGS. 2, 3A-3D, and 4A-4C show an end rate adjuster mechanisms 6 and 7incorporated into the screw 1 to provide an adjustable flow regulator.FIGS. 3A-D show a flow adjuster 6, 7 in detail comprising a flat plate14 that extends across the width of the screw trough 8 in FIG. 2 with asection of a cylinder 13 cut off to fit the shape of the screw trough 8in FIG. 2 and with a section of a cylinder 13 cut off to fit the shapeof the screw 1 with clearance 15 between the cylinder 13 and the screw1. FIGS. 4A-C show another variation of the adjustment plate 16, in theform of a vertical plate 17 with a substantially straight-across bottomcurved about a horizontal axis instead of the cylinder 13. The verticalplate 17 is cut off in the shape of the screw 1 with clearance 18.

The plates 14, 16 are adjustable along part of the length of the screw 1with clearance 18, and may also be vertically adjustable. That is, theplates 14, 16 are adjustable along the length of the screw 1 to affectthe flow rate into the ends of the screw 1. The vertical distance 19(see FIGS. 3b and 4 b) from the top of the screw 1 through to the bottomof the strike-off plate 13, 17 at the center of the screw is on theorder of 0.1 to 0.3 times the screw diameter d. Adjustment may beprovided by any suitable conventional mechanism either manual (e.g.elongated slots and cooperating bolts) or powered (e.g. pneumatic orhydraulic cylinders).

Other applications of the special designed screw with end adjustmentplates are shown in FIGS. 5 and 6.

FIG. 5 shows a bifurcation of a one-dimensional convergence long slothopper 20 using two one-dimensional convergence intermediate hoppers 21creating two shorter slots feeding left hand/right hand screws 23 and 24on a common shaft 26 feeding a protected discharge 25 with flowcontrollers 22 at the end of each slot. This configuration allows for ahanger bearing 28 to be placed in the protected region between thehoppers 21 and consequently allows a much longer screw to diameterratio. This configuration is useful for large diameter bins.

FIG. 6 shows a one-dimensional convergence main slot outlet hopper 27with multiple slot outlets from a plurality of (more than two)intermediate one-dimensional convergence hoppers 32 feeding a variablepitch screw 30 with feed rates from each outlet adjustable with the flowrate adjusters 31 on each end of the outlets. This configuration allowsfor the fine tuning of the flow pattern from the slot outlet with theadjusters 31 to compensate for any bulk solids property changes thatmight upset the flow. It also provides for the use of multiple hangerbearings [not shown], thus extending the acceptable length of the screw30. The screw 30 feeds the material to the outlet 35.

All of the embodiments described above provide substantially uniformflow of bulk particulate material along the effective length of thescrew 1, that is providing a substantially uniform flow velocitydistribution along the slot outlet of solid particulate material flowingfrom the bin or hopper to the screw discharge 5.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. A bin or hopper discharge assembly comprising: abin or hopper having at least one bottom slot outlet of effective lengthL; at least one screw in a trough and rotatable with a screw shaft ofdiameter d and having flights with a flight diameter f, and an averagepitch P and an effective length substantially equal to L, said screwreceiving material flowing from said at least one slot outlet; at leastone discharge from said screw trough; said screw having a varyingaverage pitch, shaft diameter, and flight diameter, and an effectivelength L; and said screw constructed to correspond to the formula$\frac{{\left\lbrack {\left( f_{n + 1} \right)^{2} - \left( d_{n + 1} \right)^{2}} \right\rbrack P_{n + 1}} - {\left\lbrack {\left( f_{n} \right)^{2} - \left( d_{n} \right)^{2}} \right\rbrack P_{n}}}{\left( {P_{n} + P_{n + 1}} \right)/2} = \frac{\left( {f_{L}^{2} - d_{L}^{2}} \right)P_{L}}{L}$

where f_(n), d_(n), and P_(n) are the flight diameter, shaft diameterand pitch of said screw at the nth pitch increment along the length L,and f_(L), d_(L), and P_(L) are the flight diameter, shaft diameter, andpitch of the last or final pitch increment under the flow outlet nearsaid screw discharge.
 2. An assembly as recited in claim 1 furthercomprising at least one flow rate adjuster mechanism which provides flowregulation of material transported by said screw.
 3. An assembly asrecited in claim 2 wherein said adjuster mechanism comprises asubstantially vertical plate with a substantially straight-across bottomcurved about a horizontal axis, and adjustable over a part of the lengthof the screw.
 4. An assembly as recited in claim 2 wherein said adjustermechanism comprises a substantially vertical plate with a bottom withtwo-dimensional curvature and adjustable over a part of the length ofthe screw.
 5. An assembly as recited in claim 1 wherein said at leastone screw consists of a single screw, and wherein said at least one slotoutlet consists of a single slot outlet, and wherein said at least onedischarge consists of a single discharge.
 6. An assembly as recited inclaim 2 wherein said screw has front and back ends; and wherein said atleast one flow rate adjustment mechanism comprises an adjustmentmechanism at each of said front and back ends.
 7. An assembly as recitedin claim 5 further comprising at least one flow rate adjuster mechanismwhich provides flow regulation of material transported by said screw. 8.An assembly as recited in claim 7 wherein said screw has front and backends; and wherein said at least one flow rate adjustment mechanismcomprises an adjustment mechanism at each of said front and back ends.9. An assembly as recited in claim 1 wherein said at least one slotoutlet comprises first and second slot outlets; and wherein said atleast one screw comprises a right hand screw cooperating with said firstslot outlet and a left hand screw cooperating with said second slotoutlet, said screws on a common shaft.
 10. An assembly as recited inclaim 9 wherein said at least one discharge comprises a single commonprotected discharge between said first and second slot outlets.
 11. Anassembly as recited in claim 10 further comprising a hanger bearing forsaid shaft adjacent said protected discharge.
 12. An assembly as recitedin claim 10 wherein said first and second slot outlets are inintermediate one-dimensional hoppers beneath a larger long slot outlethopper with one-dimensional convergence.
 13. An assembly as recited inclaim 10 further comprising a flow rate adjuster mechanism adjacent anend of each screw opposite said common discharge.
 14. An assembly asrecited in claim 13 wherein each of said flow rate adjuster mechanismscomprises a substantially vertical plate with a substantiallystraight-across bottom curved about a substantially horizontal axis, andadjustable over a part of the length of the screw, and verticallyadjustable; or wherein each of said flow rate adjuster mechanismscomprises a substantially vertical plate with a bottom with atwo-dimensional curvature, and adjustable over a part of the length ofthe screw, and vertically adjustable.
 15. An assembly as recited inclaim 1 wherein said bin or hopper has one-dimensional convergence. 16.An assembly as recited in claim 1 wherein said at least one screwconsists of a single screw, and wherein said at least one slot outletcomprises more than two slot outlets from more than two intermediateone-dimensional convergence hoppers beneath a larger long slot outlethopper with one-dimensional convergence, said more than two slot outletscollectively having said effective length L, said more than two slotoutlets each cooperating with said single screw.
 17. An assembly asrecited in claim 16 wherein said at least one discharge comprises asingle discharge.
 18. An assembly as recited in claim 17 furthercomprising a flow rate adjuster mechanism associated with each of saidmore than two slot outlets.
 19. An assembly as recited in claim 1wherein said bin or hopper has one-dimensional convergence and contains,and feeds with a substantially uniform flow velocity distribution alongsaid slot outlet, coal, wood, chips, plastic pellets, sugar, or drinkmixes.
 20. An assembly as recited in claim 1 wherein said screw hasflights extending beyond said effective length L.
 21. A bin or hopperassembly comprising: a bin or hopper having at least one bottom slotoutlet of effective length L; at least one screw in a trough forreceiving material from said at least one slot outlet and having aneffective length substantially equal to L; said at least one screwrotatable with a screw shaft having a diameter, and having flights witha flight diameter, and an average pitch; a single discharge from said atleast one screw trough; and at least one flow rate adjuster mechanismwhich provides flow regulation of material transported by said screw;and wherein said adjuster mechanism comprises a substantially verticalplate with a substantially straight-across bottom curved about ahorizontal axis, and adjustable over a part of the length of the screw.22. An assembly as recited in claim 21 wherein said bin or hopper hasone dimensional convergence and contains, and feeds with a substantiallyuniform flow velocity distribution along said slot outlet, coal, wood,chips, plastic pellets, sugar, or drink mixes.
 23. An assembly asrecited in claim 21 wherein said screw shaft diameter, flight diameter,and average pitch vary along said length of said shaft so as to providesubstantially uniform material flow velocity distribution along saidslot outlet.
 24. An assembly as recited in claim 23 wherein said flowrate adjuster mechanism is located above said at least one screw.
 25. Anassembly as recited in claim 23 wherein said flow rate adjustermechanism varies said effective length L of said at least one slotoutlet.
 26. An assembly as recited in claim 21 wherein said flow rateadjuster mechanism is located above said at least one screw.
 27. Anassembly as recited in claim 21 wherein said flow rate adjustermechanism varies said effective length L of said at least one slotoutlet.
 28. A bin or hopper assembly comprising: a bin or hopper havingat least one bottom slot outlet of effective length L; at least onescrew in a trough for receiving material from said at least one slotoutlet and having an effective length substantially equal to L; said atleast one screw rotatable with a screw shaft having a diameter, andhaving flights with a flight diameter, and an average pitch; a singledischarge from said at least one screw trough; and at least one flowrate adjuster mechanism which provides flow regulation of materialtransported by said screw; and wherein said adjuster mechanism comprisesa substantially vertical plate with a bottom with a two-dimensionalcurvature and adjustable over a part of the length of the screw.
 29. Anassembly as recited in claim 28 wherein said bin or hopper has onedimensional convergence and contains, and feeds with a substantiallyuniform flow velocity distribution along said slot outlet, coal, wood,chips, plastic pellets, sugar, or drink mixes.
 30. An assembly asrecited in claim 28 wherein said screw shaft diameter, flight diameter,and average pitch vary along said length of said shaft so as to providesubstantially uniform material flow velocity distribution along saidslot outlet.